1. Field of the Invention
The present invention relates to a network system including a plurality of buses formed from a plurality of nodes connected to each other with transmission control signal channels each capable of transmitting a mixture of a control signal and on information signal.
2. Description of Related Art
Recently, networking many computers and their peripheral devices or AV devices connected to each other has become more and more popular. Each of the devices connected in the network system is called a xe2x80x9cnodexe2x80x9d and incorporates an interface for connection thereof to the network system.
The construction of a conventional network system is illustrated by way of example in FIG. 1. The network system is generally indicated with a references numeral 300. As seen, it comprises a plurality of buses 301 each formed from a plurality of nodes 303 connected to each other with a transmission control channel. The buses 301 are connected to each other with bridges 302.
A signal channel designed in conformity to the serial interface standard IEEE 1394 may be used as the transmission control signal channel. Under the standard IEEE 1394, one bus 301 may have a maximum of 63 nodes connected thereto. When more than 63 nodes are to be connected in one bus 301, more than one bus 301 has to be provided and such buses must be connected to each other with bridges 302. The standard IEEE 1394 prescribes that a large-scale network may be organized using a maximum of 1,023 buses. Also under the IEEE 1394, interconnection of the buses and bus ID assignment should be done automatically. The procedure of the bus ID assignment is called a xe2x80x9cconfigurationxe2x80x9d. When a bus or buses is added to or deleted from an existing network system, the configuration is started and executed on the entire network system.
FIG. 2 shows a simplified network system model in which 9 buses in total are connected to each other with bridges. Bus ID #0 to #8 are assigned to the buses, respectively. Portals included in different buses are provided at opposite ends of each bridge, and each of the portals has a register intended for discrimination of an ID No. of a destination bus. The bridge connecting a bus of ID #0 and a one of ID #1 is taken here for example. One of the portals has a register in which a lower bound of 1, upper bound of 5 and rte of 2 are set for a destination bus ID (D). Namely, these parameters define a requirement of 1xe2x89xa6Dxe2x89xa65. The other portal has a register in which a lower bound of 1, upper bound of 5 and rte of 3 are set for a destination bus ID (D). These parameters define a requirement of D less than 1 and 5 less than D. Thus, when the destination bus ID given to a packet which is to be sent from the bus of ID #0 is over 1 and under 5, the bridge will pass the packet to the bus of ID #1. If the destination bus ID imparted to a packet to be sent from the bus of ID #1 is under 1 and over 5, the bridge will pass the packet to the bus of ID #0.
rte is also defined to be 0 and 1 in addition to 2 and 3. Briefly, rte=0 means xe2x80x9cdisablexe2x80x9d, rte=1 means xe2x80x9creservexe2x80x9d, rte=2 means lowerxe2x89xa6Dxe2x89xa6upper, and rte=3 means D less than lower and upper less than D. When rte=0, no packet will be transferred.
When the buses included in a network system have been increased in number, some buses will be deleted from the network system while some new buses are additionally introduced into the network system. The bus deletion and addition are frequently done. At each time, the whole network system has to be subjected to a configuration, which will cause a frequent interrupt of data transmission in the network system. Also, the reconfiguration will possibly lead to failure of a network component or node and missing of data, The computer and its peripheral devices are required to have a specially high reliability. Therefore, if the network system is reconfigured frequently, the computer and devices will possibly operate with no stability. Such frequent reconfiguration is not desirable of course.
In a large-scale network system including many buses, there is a high possibility that buses are connected to each other using a circuit-connected type channel as in public telephone network or a channel as in radio communications in which circuit connection is so unstable that the circuit is abruptly discontinued or reconnected. In such a case, the network system will possibly be reconfigured frequently and thus will be very unstable.
Also the network will not always operate in complete accordance with the standard since a node or bridge will possibly malfunction or be faulty. This will also cause the network system operation to be unstable.
It is therefore an object of the present invention to provide a network system in which less configuration is required when the bus topology has changed.
According to the present invention, there is provided a network system including a plurality of subnetworks each formed from at least a bus in which at least a node is connected via a common transmission control signal channel, a first bridge holding first flags for the number of buses in the subnetworks and second flags for the number of subnetworks, and a second bridge connecting the subnetworks and holding flags for the number of subnetworks.
According to another aspect of the present invention, the first bridge includes means for comparing a destination ID of a packet data from the node and the first and second flags to judge, based on the two flags, whether the packet data is to be transferred to any other bus, and means for outputting the packet data corresponding to the result of the comparison from the comparing means.
According to another aspect of the present invention, the second bridge includes means for comparing a destination ID of a packet data from the node and the first and second flags to judge, based on the two flags, whether the packet data is to be transferred to any other bus, and means for outputting the packet data corresponding to the result of the comparison from the comparing means.
According to another aspect of the present invention, the first bridge includes two input/output means for connection to one bus and any other bus, respectively. The second bridge includes two input/output means for connection to one subnetwork and any other subnetwork, respectively. Furthermore, the second bridge may include more than three input/output means for connecting more than three subnetworks.